It is desirable that a chemical material is industrially excellent in storage stability, and does not show a change in form or property even when stored for a long time. In general, a polysiloxane having a reactive functional group such as a (meth)acryloyl group may be partially crosslinked, and may show a decrease in solubility in an organic solvent (or may become insoluble in an organic solvent) during storage singly. When the polysiloxane is stored as a polymer solution, a gel of the polysiloxane may be generated, or an insolubilized component may be precipitated in the solution. In particular, unfavorable failure is that gelation or insolubilization is occurred after the polysiloxane synthesis process (e.g., concentration process or dilution process), and the target product is not obtained.
Patent Literature 1 discloses a method for producing a polysiloxane macromonomer having a reactive functional group such as a (meth)acryloyl group. Patent Literature 1 states that condensation may be progressed with time, and a gel or the like may be generated when subjecting an alkoxysilane to hydrolysis and condensation using a catalyst that is dissolved in the system. Patent Literature 1 also states that it is possible to use an organic solvent such as an alcohol, a ketone, and an ether during the production process, but it is preferable to remove the organic solvent from the system during or after the production process, and that a polymer may precipitate when an alcohol produced as a by-product during condensation or the organic solvent remains in the system.
Patent Literature 2 discloses a method for producing a reactive polysiloxane which has a reactive functional group such as a (meth)acryloyl group, and is capable of being dissolved in an organic solvent. The method includes the following six processes.
First step: A raw material containing an organosilicon compound A1 having a (meth)acryloyl group and a hydrolyzable group, and a silicon compound B1 in which four siloxane bond-forming groups are bonded to the silicon atom, is subjected to hydrolysis and copolycondensation under alkaline conditions so that the amount of the silicon compound B1 is 0.3 to 1.8 mol based on 1 mol of the organosilicon compound A1.Second step: The reaction liquid obtained by the first step is neutralized using an acid.Third step: A volatile component is removed from the neutralized liquid obtained by the second step.Fourth step: A concentrate obtained by the third step is mixed with (brought into contact with) an organic solvent for water washing to dissolve at least the condensation product in the organic solvent for water washing.Fifth step: An organic liquid obtained by the fourth step is washed with water to obtain an organic solution containing the condensation product.Sixth step: A volatile component is removed from the organic solution obtained by the fifth step.
Patent Literature 2 states that it is preferable to use an organic solvent that can dissolve the condensation product, and is easily separated from water as the organic solvent for water washing used in the fourth step. And is described that preferable organic solvent for water washing is a ketone such as methyl isobutyl ketone, an ether such as diisopropyl ether, an aromatic hydrocarbon such as toluene, an aliphatic hydrocarbon such as hexane, an ester such as ethyl acetate, and the like.
Patent Literature 2 describes that a curable composition can be prepared when an organic solvent and an additional component are added to the condensation product (reactive polysiloxane) obtained by the sixth step. In the Patent Literature 2, an alcohol such as ethanol and isopropyl alcohol, an alkylene glycol monoalkyl ether such as propylene glycol monomethyl ether, an aromatic compound such as toluene and xylene, an ester such as propylene glycol monomethyl ether acetate, ethyl acetate, and butyl acetate, a ketone such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, an ether such as dibutyl ether, and N-methylpyrrolidone are described as examples of the organic solvent that can dissolve the condensation product (reactive polysiloxane).
If ethyl acetate is used as the organic solvent for water washing and as the organic solvent used to prepare the curable composition in Patent Literature 2, a solution composition can be produced without removing the organic solvent for water washing in the sixth step, and adding an organic solvent differing from the organic solvent for water washing to prepare a curable composition (solvent substitution step). This makes it possible to reduce the amount of energy, the production cost, and the production time when producing a curable composition. However, when coating an article with the resulting curable composition, it is necessary to select a compound that does not erode the surface of the article as the organic solvent used to prepare the curable composition. Therefore, the type of organic solvent is limited. For example, ethyl acetate erodes a substrate containing polycarbonate or the like and is not favorable. It was surprisingly found that a curable composition that is prepared using ethyl acetate as an organic solvent for water washing, and is not subjected to a solvent substitution step, tends to generate a gel during long-term storage.
As described above, a reactive polysiloxane which has a reactive functional group and is capable of being dissolved in an organic solvent, and a method for producing such a reactive polysiloxane are known in the art. A method in which a reactive polysiloxane is diluted with an organic solvent to prepare a polymer solution, and a method in which an additional component is added to a polymer solution to prepare a curable composition are also known in the art. Since different functions or properties are required for the organic solvent for water washing and the diluting organic solvent, it may be impossible to use a common organic solvent as the organic solvent for water washing and the diluting organic solvent.